using System;

using System.Linq;

​

public static class Program

{

    public static void Main()

    {

        var phoneNumber = "905547295555";

        phoneNumber = phoneNumber.Reverse().Substring(0,10).Reverse();

        Console.WriteLine(phoneNumber);

    }

     public static string Reverse(this string s)

    {

        var charArray = s.ToCharArray();

        Array.Reverse(charArray);

        return new string(charArray);

    }

}